The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Hybrid powertrain systems employ internal combustion engines and other non-combustion torque machines to provide tractive torque to propel a vehicle. The non-combustion torque machines use non-fuel power sources, e.g., high-voltage batteries. One powertrain operating strategy includes operating the powertrain using only the non-combustion torque machine to provide the tractive torque. This includes operating the powertrain with the internal combustion engine shut off. This may include automatically shutting off the internal combustion engine during ongoing powertrain operation. This may include operating the hybrid powertrain with the internal combustion engine shut off, and only starting the internal combustion engine when available power from the non-fuel power source is less than a threshold.
Internal combustion engines generate heat and exhaust gases as byproducts of combustion. Known exhaust aftertreatment devices include catalytic materials that react with the exhaust gases at temperatures greater than ambient to oxidize or reduce constituents to inert gases prior to their release into the atmosphere. A portion of the heat generated by the engine is transferred to the exhaust aftertreatment devices, and a portion is lost into the atmosphere. It is known that an exhaust aftertreatment device must reach a threshold temperature to effectively catalyze, filter adsorb, desorb or otherwise treat exhaust gas constituents. One threshold temperature is referred to as a light-off temperature, which indicates exothermic reactions are occurring in the exhaust aftertreatment device. It is known that engine exhaust emissions are greater prior to light-off in an exhaust aftertreatment device. It is preferred to reduce the time to light-off an exhaust aftertreatment device subsequent to starting an internal combustion engine to reduce engine exhaust emissions.
Known heat engines including Stirling-cycle engines are closed-cycle regenerative devices that convert heat to mechanical work by cyclically compressing and expanding a fixed quantity of a working fluid using temperature differentials.